The Effects of Turbidity on Suspension Feeding Bivalves

This thesis aimed to describe the relationship between suspended sediment concentration stimulating the turbidity caused by natural events or human activities, and the feeding behaviour and energetics of scallops (Pecten novaezelandiae), mussels (Perna canaliculus) and pipis (Paphies australis). A wide range of suspended sediment concentration with different organic content was used. In experiment 1, sediment with high organic content added to natural seston (12 - 733 mg 1−1) was used, whereas in experiment 2, sediment with very low organic content added to natural seston (20 - 196 mg 1−1) was used. Scallops enhanced the organic content of ingested matter by producing pseudofaeces with low organic content when the diet organic content had been diluted to~ 14% in both experiments. For the diet with high organic content, the clearance rate (the volume of water cleared of suspended particles) decreased with increasing sediment concentration (12 - 733 mg 1−1) ,but when the diet was composed of low organic content, clearance rate increased up to a concentration limit of 120-140 mg 1−1. Positive scope for growth was attained until suspended sediment concentration exceeded 190 mg 1−1. Similarly, mussels also enhanced the organic content of ingested matter by producing pseudofaeces with low organic content when the diet organic content had been diluted to ~ 16% in both experiments. The enhancement of ingested organic fraction was accomplished by two different feeding behaviours. When the diet had high organic content, mussels clear less water, reduce the volume of pseudofaeces produced, and reduce the amount of energy expired via low respiration rates. Consequently, the net energy gained was uniformly high as sediment concentrations increased to 322 mg 1−1. The low organic diet prompted high clearance rates and increase in pseudofaeces production as sediment concentration increased. Due to high feeding activities, energy expenditure was also high which was reflected in a low net energy gain. Pipis can only feed efficiently at very low sediment concentrations (